It is known that thermoplastic elastomers can be formed having chemically different polymer blocks for providing various desirable properties. In one common form, styrenic block copolymers (SBCs) can be formed having internal blocks of conjugated diene and external blocks having aromatic alkenyl arene. The elastomeric properties of internal conjugated diene blocks along with the “harder” aromatic alkenyl arenes external blocks together provide the resulting block copolymer distinctive properties for use in a large variety of applications.
It is also known that SBC's can be functionalized with functional groups such as sulfonic acid in order to further modify their characteristics. One of the first such sulfonated block copolymers is disclosed, for example, in U.S. Pat. No. 3,577,357 to Winkler. The resulting block copolymer was characterized as having the general configuration A-B-(B-A)1-5, wherein each A is a non-elastomeric sulfonated monovinyl arene polymer block and each B is a substantially saturated elastomeric alpha-olefin polymer block, said block copolymer being sulfonated to an extent sufficient to provide at least 1% by weight of sulfur in the total polymer and up to one sulfonated constituent for each monovinyl arene unit. The sulfonated polymers could be used as such, or could be used in the form of their acid, alkali metal salt, ammonium salt or amine salt. According to Winkler, a polystyrene-hydrogenated polyisoprene-polystyrene triblock copolymer was treated with a sulfonating agent comprising sulfur trioxide/triethyl phosphate in 1,2-dichloroethane. The products are described as having water absorption characteristics that might be useful in water purification membranes and the like.
More recently, U.S. Pat. No. 7,737,224 to Willis et al. disclosed the preparation of sulfonated polymer and inter alia illustrated a sulfonated block copolymer that is solid in water comprising at least two polymer end blocks and at least one saturated polymer interior block wherein each end block is a polymer block resistant to sulfonation and each interior block is a saturated polymer block susceptible to sulfonation, and wherein the interior blocks are sulfonated to the extent of 10 to 100 mol percent. The sulfonated block copolymers are described as having a high water vapor transport rate while at the same time having good dimensional stability and strength in the presence of water, and as being therefore valuable for many end use applications, especially where the combination of good wet strength, good water and proton transport characteristics, good methanol resistance, easy film or membrane formation, barrier properties, control of flexibility and elasticity, adjustable hardness, and thermal/oxidative stability are important.
Additionally, US 2010/0048817A1 to Dado et al. discloses a process for preparing sulfonated block copolymers illustrating, e.g., a process which involves providing a precursor block copolymer having at least one end block A and at least one interior block B wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation wherein said A and B blocks are substantially free of olefinic unsaturation; and reacting the precursor block copolymer with an acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent to form a sulfonated block polymer.
In particular, Dado et al. disclose that the solvents used for the preparation of the sulfonated block copolymer include a first non-halogenated solvent, the most preferred being cylcohexane, methylcyclohexane, and a second non-halogenated solvent which is chosen such that it is miscible with the first solvent, but is a poor solvent for the sulfonation susceptible block, the most preferred being n-heptane. The product obtained in the process is described as comprising sulfonated polymer micelles and/or other polymer aggregates of definable size and distribution, as would be characteristic of polymer micelle structures.